So,
First of all, we should remember the following:
In this case, we have the following transformation:
[tex]f(x)=\sqrt[]{x}\to g(x)=3\sqrt[]{x}[/tex]
As you can see, we're multiplying the function f by 3. So, this is an example of a vertical stretch of the function f by a factor of 3. So the answer is B.
